【单点】每日突破，MapReduce自定义InputFormat

// 初始化资源，一般用于打开IO流
// 常用IO流为FSDataInputStream，默认会定义在成员变量中：inputStream
public void initialize(InputSplit split,
                                  TaskAttemptContext context
                                  ) throws IOException, InterruptedException
{
	FileSplit fs = (FileSplit) split;
	Path path = fs.getPath();
	FileSystem fileSystem = path.getFileSystem(context.getConfiguration());
	inputStream = fileSystem.open(path);
}

// 关闭资源，一般用于关闭IO流
public void close() throws IOException {
	IOUtils.closeStream(inputStream);
}

// 类似于指针，如果要读取的数据存在，返回true，否则返回false
public boolean nextKeyValue() throws IOException, InterruptedException {
}

// 获取当前行的key
public KEYIN getCurrentKey() throws IOException, InterruptedException;
  
// 获取当前行的value
public VALUEIN getCurrentValue() throws IOException, InterruptedException;

// 返回数据读取进度，0-1
public float getProgress() throws IOException, InterruptedException;

job.setInputFormatClass();